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arXiv 2407.06308cond-mat.supr-concond-mat.other
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自旋-3/2核磁共振:对齐体系的精确解及其对探测铁基超导体的意义

Spin-3/2 nuclear magnetic resonance: Exact solutions for aligned systems and implications for probing Fe-based superconductors

Jaafar N. Ansari, Karen L. Sauer

AI总结:

本文解析求解了自旋-3/2核磁共振在电场梯度对齐时的谱,给出拉比频率与EFG不对称性的关系,并应用于铁基超导体粉末样品,简化提取内磁场等关键参数。

摘要:

基于虚构自旋-1/2形式体系,解析地发展了在静磁场与电场梯度(EFG)主轴之一对齐时自旋-3/2原子核的核磁共振(NMR)谱。推导了本征态和跃迁频率以及共振激发后磁矩期望值的紧凑闭式表达式。重点在于定义和解释相关的拉比频率,作为激发方向和椭圆率的函数。发现跃迁根据其对激发方向的敏感性天然分为两个子集,其中一个子集的拉比频率直接依赖于EFG的不对称性。一个自然的应用是研究铁基超导体,其在低温下的反铁磁有序导致与EFG主轴对齐的强内禀磁场。分析了两种此类铁基超导体BaFe$_2$As$_2$和CaFe$_2$As$_2$粉末样品的零外场NMR谱,并例证了提取内磁场、四极耦合常数和EFG不对称参数的简便性,这些参数对于研究磁有序、结构性质、相变和NMR动力学至关重要。结果与通过旋转单晶进行的常规高场NMR实验相比具有优势。总体而言,精确而简洁的表达式所提供的物理洞察将有助于轻松解释自旋-3/2谱,并促进新的实验方向。

英文摘要:

The nuclear magnetic resonance (NMR) spectrum of spin-3/2 nuclei in a static magnetic field aligned with one of the electric field gradient (EFG) principal axes is developed analytically, based on fictitious spin-1/2 formalism. Compact closed-form expressions for the eigenstates and transitions frequencies, as well as the expectation value of the magnetic moment after resonant excitation, are derived. Emphasis is placed on defining and interpreting the associated Rabi frequencies, as a function of excitation direction and ellipticity. It is found transitions inherently fall into two subsets, depending on their sensitivity to excitation direction, with the Rabi frequency of one subset directly depending on the asymmetry of the EFG. A natural application is the study of Fe-based superconductors, whose antiferromagnetic ordering at low temperatures leads to a strong intrinsic magnetic field aligned with the EFG principal axes. Zero external-field NMR spectra, from powder samples of two such Fe-based superconductors, BaFe$_2$As$_2$ and CaFe$_2$As$_2$, are analyzed and exemplify the simplicity in extracting the internal magnetic field, the quadrupole coupling constant, and the EFG asymmetry parameter, which are important for studying magnetic ordering, structural properties, phase transitions, and NMR dynamics. Results compare favorably to conventional high-field NMR experiments done with the rotation of single crystals. Overall, the physical insights, afforded by the exact and concise expressions, will lead to ready interpretation of spin-3/2 spectra as well as precipitate new experimental directions.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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